1. Field of the Invention
The present invention relates to an ink-jet recording apparatus for recording by emitting ink, an ink-jet recording method, an image processing apparatus for processing an image to be recorded, and a method of outputting data from a host device connected to an ink-jet recording apparatus.
More particularly, the present invention relates to an ink-jet recording apparatus, an ink-jet recording method, and an image processing apparatus based on the technique of recording by quantizing data to three or more levels and then mapping the quantized data to L.times.M matrices.
2. Description of the Related Art
Various color recording techniques are known in the art. They include a thermal transfer recording technique in which recording is performed by transferring ink from an ink ribbon by means of thermal energy, and an ink-jet recording technique in which recording is performed by firing an ink droplet to a recording medium such as paper.
Of these various techniques, the ink-jet recording technique has the advantages of low noise, low running cost, small size, and the capability of easily forming a color image. In view of these advantages, the ink-jet recording technique is used in a wide variety of applications such as a printer, copying machine, etc.
The recent trend in the technology of the ink-jet recording apparatus is that recording liquid droplets with a smaller size are employed to achieve a higher resolution thereby achieving high quality in recorded images.
However, as the resolution becomes high, the data to be processed becomes exceedingly large. As a result, a longer time is required for a host computer to process the data and transfer the resultant data to a recording apparatus. This causes great reduction in the total throughput of the system.
One known technique to solve the above problem is to employ a matrix pattern in the recording process. In this technique, a host computer processes data with a relative low resolution and a rather large number of quantization levels and outputs the resultant data to a printer which in turn converts the received data into a matrix form and. performs recording in accordance with the matrix data. For example, a host computer quantizes image data to 5-level (3-bit) data with a resolution of 300.times.300 dpi, and the printer converts the data received from the computer to bilevel data with a resolution of 600.times.600 dpi (in a 2.times.2 matrix form). In this case, the host computer is required only to process data with a resolution as low as 300 dpi, and thus the burden of the host computer is reduced. Furthermore, the data to be transferred from the host computer to the printer is reduced in size to a value corresponding to 300.times.300 dpi each represented by 3 bits, which is only 75% of the data size required for bilevel data of a resolution of 600.times.600 dpi. This technique based on the matrix pattern is useful particularly for dealing with images such as photographs in which representation of halftone is more important than sharpness at edges in contrast to graphical images or graphs in which sharpness is more important.
When an image is recorded on plain paper serving as a recording medium by means of the ink-jet recording technique, the water resisting property of the recorded image is not good enough. When a color image is recorded using the ink-jet recording technique, it is difficult to meet simultaneously both requirements of small feathering in a high-density image and small bleeding between different colors. In other words, the problem of the conventional ink-jet recording technique is that it is difficult to obtain a color image that simultaneously satisfies both requirements of high quality and high durability.
One known technique of improving the resistance of printed images to water is to employ an ink containing a color material having resistance to water. Although the ink of this type is practically used recently, the property of resistance to water is not sufficient. Besides, because such an ink hardly dissolves in water after being dried, the nozzles of the recording head are easily clogged with dried ink. A complicated mechanism is required to prevent the nozzles from being clogged.
There are a large number of known techniques for improving the durability of a recorded image.
For example Japanese Patent Laid-Open No. 58-128862 discloses an ink-jet recording technique in which the positions of dots at which ink will be fired are determined before starting to record an image, and a recording ink and a processing ink are fired at the same dots. In this technique, drawing may first be performed with processing ink before the operation using a recording ink, or the processing ink may be used after the image was drawn using the recording ink so that the processing ink is put on the dots formed by the recording ink. Furthermore, the processing ink may again be put on the top of the dots formed by putting the recording ink on the bottom layer of processing ink. In Japanese Patent Laid-Open No. 8-52867 filed by the present applicant. there is disclosed an ink-jet recording technique in which a processing liquid is applied to every predetermined number of pixels. Japanese Patent Laid-Open No. 9-226154 discloses a technique in which a processing liquid is applied to all inked dots located at edges of a printed image while the processing liquid is applied to every predetermined number of inked dots at the other locations thereby achieving high resistance to water using the minimum amount of processing liquid.
However, if the processing liquid is applied to all inked dots detected at edges of an image to ensure the application of the processing liquid, the amount of the processing liquid applied to dots can become too much depending on the image recorded. Such an excessive application of the processing liquid results in an increase in running cost and can cause the recorded image to have distortion due to absorption of water into paper. These disadvantages in the conventional techniques are described in further detail below with reference to FIG. 18.
In a specific example shown in FIG. 18, an image is formed with an array of 600-dpi pixel. In other words, each pixel has a size of about 42 .mu.m. A processing liquid expands on paper and forms a dot with a diameter of about 80 .mu.m. Because the processing liquid expands over an area greater than a pixel size, it is not necessary to put the processing liquid on every pixels except for pixels located at edges of an image, and sufficiently high quality can be achieved in the printed image only by applying the processing liquid to every pair of pixels, for example. Although in FIG. 18 each inked dot forming the image has a diameter similar to the size of each pixel, the actual diameter of inked dots is usually 1.4 times the grid space so as to meet the requirement in terms of the area factor at a duty factor of 100%. To achieve a good fixing function, it is desirable to employ a processing liquid of the type exhibiting high penetration. If a processing liquid with high penetration property is used, the processing liquid penetrates, after being deposited on paper, into the paper not only in a depth direction but also in lateral directions. This allows the processing liquid deposited on paper to easily expand to a large size.
FIG. 18A illustrates an example of a recorded image in which ink is applied to those pixels in a shaded area. A processing liquid is applied to all pixels at the edges of the image while the processing liquid is applied to every pair of pixels at the other locations as shown in FIG. 18B. The pixels at the edges are extracted by detecting a transition from a non-inked pixel to an inked pixel in the horizontal direction. As can be seen from FIGS. 18A and 18B, the processing liquid is applied to only six pixels of ten inked pixels. Thus, a reduction in consumption of processing liquid is achieved. However, in the case where the recording data has a checker pattern such as that shown in FIG. 18C, all inked pixels are located at edges and thus the processing liquid is applied to all inked pixels as shown in FIG. 18D. In the specific example shown in FIG. 18D, the processing liquid is applied to all eight inked pixels. The processing liquid expands on the paper into adjacent non-inked pixels which need no processing liquid. Such an excessive application of the processing liquid causes the recording paper to be bent or cockled thus causing distortion in the recorded image. Another result of the excessive application of the processing liquid is an increase in running cost.
When data is converted to bilevel data in accordance with the error diffusion technique, it is impossible to control the manner of converting a given image to data, and therefore the resultant recorded image can include a large number of inked pixels located at edges as is the case in the example shown in FIG. 18C and thus the processing liquid is applied excessively. However, if recording is performed using matrix patterns, it is possible to control the locations of dots within each matrix.